Person besides the two primarily involved

Wikipedia Word definitions in Wikipedia
In electoral politics, a third party is any party contending for votes that failed to outpoll either of its two strongest rivals (or, in the context of an impending election, is considered highly unlikely to do so). The distinction is particularly significant ...

WordNet Word definitions in WordNet
n. someone other than the principals who are involved in a transaction a political party organized in opposition to the major parties in a two-party system

Wiktionary Word definitions in Wiktionary
n. 1 someone not directly involved in a transaction. A third entity in the Seller (first party) and Customer (second party) relationship. A Seller may employ a third party to perform specific services to augment the value of a product. For example, a manufacturer ...

Longman Dictionary of Contemporary English Word definitions in Longman Dictionary of Contemporary English
noun EXAMPLES FROM OTHER ENTRIES ▪ Both companies will meet with a neutral third party to resolve the disagreement. EXAMPLES FROM CORPUS ▪ Is it lawful to refer questions of fact and law to a third party to determine in a non-judicial fashion? ▪ It also ...